The purpose of a digital communication system is to effectively transmit and receive information over a particular channel or communication medium. To that end, the performance of any communication system is ultimately determined (and often limited) by its ability to respond to the presence of noise in the system. Digital radios often have many modes for communicating with one another, and many methods of suppressing or limiting noise within a network, such as frequency hopping, bit and frame synchronization, and numerous modulation/demodulation and filtering techniques. The Single Channel Ground-Airborne Radio System (SINGCARS) digital radio is an example of a type of radio which employs these various modes and methods of communication. Radios employing these techniques are shown in commonly assigned, copending U.S. patent application Ser. No. 08/846,885 filed on May 1, 1997 by Pries, et al., entitled "Method and Apparatus for Voice Intranet Repeater and Range Extension", Ser. No. 08/857,990 filed on May 16, 1997 by Bertrand, et al., entitled "Radio Architecture for an Advanced Digital Radio in a Digital Communication System", Ser. No. 08/861,606 filed on May 22, 1997 by Epstein, et al., entitled "Radio Remote Interface for Modulating/Demodulating Data in a Digital Communication System", and Ser. No. 08/850,231, filed on May 2, 1997 by Epstein, et al., entitled "Frequency Hopping Synchronization and Tracking in a Digital Communication System". In frequency hopping signal transmission systems, a wideband signal is generated by hopping from one frequency to another over a large number of frequency choices. The frequencies used are chosen by a code similar to those used in direct sequence systems. For general background on spread spectrum systems, reference is made to a text entitled Spread Spectrum Systems, 2nd edition, by Robert C. Dixon and published by Wiley-Interscience, New York (1984).
Despite these various techniques and synchronization schemes, situations often occur wherein a particular communication channel is jammed or becomes so noisy that an information signal transmitted over that particular channel is unintelligible at the receiver. Alternatively, a receiver may detect the presence of noise over a noisy communication channel and mistake it for an information signal. This represents a major problem for almost any communication system, but is particularly troublesome for military applications and emergency situations, where constant communication and informational updates are vital to mission success. Under such conditions, the receiver must be tuned to a different channel in order to properly receive and decode the information signal transmitted. However, network protocols such as Carrier Sense Multiple Access (CSMA) which are used within the digital radio communication system require strict adherence to system timing requirements in order to acquire and receive an information signal within a particular time interval. Therefore, it is essential not only that a different, non-noisy channel be available over which to receive an information signal, but that selection and acquisition of that channel be attained within the time constraints of the particular network protocol and system requirements utilized by an application. Consequently, it is greatly desirable to obtain an improved method for determining if a particular frequency channel is noisy and, if so, to cycle to a clear or non-noisy channel within a permissible time interval so as to maintain network continuity.